What's actually included in the IRS standard mileage rate?

The exact list baked into the rate

Per IRS Publication 463, once you've elected the standard mileage rate for a vehicle, none of these can also be deducted as separate expenses for that vehicle:

This is the flip side of the choice covered in standard mileage vs. actual expenses: the two methods aren't a menu you mix and match per line item on one car — they're two complete, mutually exclusive ways of pricing the same vehicle's business use for the year.

What you can still deduct separately

Three things fall outside the rate entirely, per Publication 463 and IRS Tax Topic 510:

• Parking fees and tolls. "In addition to using the standard mileage rate, you can deduct any business-related parking fees and tolls," per Publication 463 — confirmed directly by Tax Topic 510: these are deductible "whether you use the standard mileage rate or actual expenses." (Parking at your own place of work is a nondeductible commuting cost either way.)
• The business-use share of car loan interest. Publication 463: "if you are self-employed and use your car in your business, you can deduct that part of the interest expense that represents your business use of the car. For example, if you use your car 60% for business, you can deduct 60% of the interest on Schedule C." This applies on top of the standard mileage rate — it's not one of the excluded items above.
• The business share of state and local personal property tax on the vehicle. Publication 463: a self-employed driver "can deduct the business part of state and local personal property taxes on motor vehicles on Schedule C... even if you use the standard mileage rate."

Why this trips drivers up

The instinct to save every gas receipt is reasonable — it's exactly right for a driver using the actual-expense method. It's just the wrong instinct once you've elected standard mileage for that vehicle, where the receipts don't add a second deduction; they duplicate one already priced into the per-mile rate. The two methods are also locked by an earlier choice: per Publication 463, choosing standard mileage in a car's first year of business use keeps the option to switch later, but choosing actual expenses in year one locks that vehicle out of standard mileage for good.

Not to be confused with your real cost per mile

Keep this separate from what a mile actually costs you to drive, which is a different number entirely — AAA's real-world figure for depreciation, fuel, insurance, and maintenance on an actual vehicle, currently in the high-60¢-to-around-$1-per-mile range depending on annual mileage. The IRS rate is a flat tax allowance set once a year; your true cost is specific to your car and changes with how you drive it. The two numbers happen to sit in a similar range some years, which is exactly what makes people assume they're the same figure. They aren't measuring the same thing.